1. Field of the Invention
This invention relates to apparatus and methods used in specialized, minimally invasive surgery, and more particularly to techniques for minimizing the amount of fluid absorbed within a patient during surgeries utilizing irrigation flows.
2. Description of Related Art
Laparoscopic techniques for performing certain surgical procedures have been widely adopted because they often simplify a given operation, reduce the trauma to the patient, and shorten recovery time. In procedures such as hysteroscopy and prostatectomies using trans-urethral resection, the operative site must be constantly irrigated as the surgeon views the site through an endoscope while manipulating the laparoscopic instruments. Irrigation is essential not only to visualization, but also to transporting surgical debris, blood and tissue, away from the site. However, as pointed out in U.S. Pat. No. 5,492,537 to Vancaillie ("the '537 patent"), there are problems associated with such procedures. Because some of the fluid will be absorbed in the body instead of being transported away, there is a danger of pulmonary edema or electrolytic imbalance if too much fluid is absorbed. Consequently, the '537 patent discloses a fluid monitoring system which determines, on an ongoing basis, the amount of fluid absorbed by measuring the mass of fluid supplied from a source and the mass of fluid collected from the operative site. If indications are that too much fluid is being absorbed, measures can be taken.
The system of the '537 patent operates by using gravity to feed irrigation fluid from an elevated source to a fluid source channel in the probe used by the surgeon to observe the operative site. Concurrently, irrigation fluid is collected from the operative site via a fluid collection channel in the probe, while overflow from the operative site proceeds outwardly through the body orifice into a fitted drape system feeding a funnel-like drain bag. The fluid from the collection channel and drain bag is drawn into collection canisters by a common negative pressure source for disposal or examination. By monitoring the weight of the source fluid delivered and waste fluid collected, the system can calculate an approximate value for fluid absorbed.
A high irrigation flow rate is needed to insure full lavage and adequate visibility at the operative site. To minimize absorption of fluid within the patient and the passage of fluid from intravascular to interstitial spaces, outflow of fluid through the probe's collection channel (and therefore the negative pressure or suction level in the channel) must be substantial and continuous. In practice, however, this result is not readily achieved. Where the suction force in the probe collection channel and the drain bag are produced by the same negative pressure source, as in the '537 patent, suction forces generated by the negative pressure source are often powerful enough to keep the drain bag empty. As a result, the open drain line and empty drain bag can draw large quantities of air, taxing the suction capabilities of the negative pressure source and reducing the suction force in the probe collection channel and at the probe tip. Consequently, suction at the operative site can be partially lost, resulting in both excessive fluid absorption in the body and diversion of excess fluid into the drain bag.